COMPARISON OF ACIDS. 



25 



temperatures, and has a fishy odour. It forms a hexa-brom- 

 compound melting at 177 C. 



Comparison of the Acids ol the four Series. The following table 

 (VII.) will show the main differences between stearic, oleic, linolic, 

 and linolenic acids, the corresponding members of the four 

 series : 



TABLE VII. COMPARISON OF THE FOUR TYPICAL FATTY ACIDS. 



Hardened Fats. When fats containing unsaturated acids are 

 mixed with a suitable catalyst, finely divided nickel being the 

 most favoured, they absorb hydrogen when passed through at 

 a suitable temperature, and all unsaturated acids will eventu- 

 ally be converted to stearic or an acid of this series. The melting 

 point of the oil or fat rises during hydrogenation, and the sub- 

 stances which give rise to certain colour reactions (e.g., Halphen 

 and Baudouin tests), as well as those to which taste and smell 

 are due, disappear. 



These hardened fats may be used as constituents of 

 margarine and adulterants of butter. The phytosterol of 

 vegetable oils is, however, not changed, and the presence of 

 nickel in minute amounts would indicate the use of hardened fat. 



